Re: Inline ASM and stack/base pointer

[kevin diggs <diggskevin38 at gmail dot com>]

Hi,

On Thu, Jun 9, 2011 at 12:49 PM, Ian Lance Taylor <iant@google.com> wrote:
> Daniel Mierswa <impulze@impulze.org> writes:
>
>> I was wondering how to overcome the issue that evolves when parameters
>> (inputs) to the inline assembly are passed relative to ebp/esp and
>> modifying those pointers in the inline assembly. Basically
>> __asm__("push %ecx\nmov %0, %edx\n"::"m"(variable)); could set '%0' to
>> 4(%esp) or similar which would no longer represent the same location
>> once I use push/pop in my asm. Is it possible to explicitly state that
>> GCC passes those relative to esp _or_ ebp so I can safely modify at
>> least one pointer (i.e. reserve stack space)? Or are there any other
>> ways to overcome this issue? Thanks in advance.
>
> Add "%esp" to your clobber list. ?That should force the compiler to pass
> any stack variables using an offset from %ebp.
>
> Ian
>

What happens if you use -fomit-frame-pointer?

If you muck with esp, do you have to put it back? In other words if
you include "%esp" in your clobber, does the compiler back up and
restore it?

Thanks!

kevin